In certain indirect printing systems, an ink image is applied onto an image transfer medium, and this image is then transferred to a second substrate, typically without the application of heat. The image can be transferred using minimal or low pressure applied to the back surface of the transfer medium, after which the medium is removed. The first step in the transfix process requires printing the liquid ink onto the image transfer medium, which typically occurs by directing ink droplets onto the surface of the medium. In this step it is necessary for the ink to sufficiently wet the surface of the transfer medium so that the ink droplet does not drawback in an uncontrolled or random manner. Excessive ink drawback significantly reduces transfixed image quality since the droplet is either randomly spread onto the substrate or fails to transfer properly.
Another aspect of the aqueous transfix process is that the ink becomes partially dried before being transfixed, so the partially dried ink must still be able to transfer easily and completely from image transfer medium to substrate, leaving very little residue behind. Thus, the surface of the image transfer medium must juggle two generally mutually exclusive characteristics—surfaces which are sufficiently wettable tend to resist transfer of the ink to the substrate and surfaces that have good transfer characteristics tend to resist wetting.
There is a need for an aqueous image transfer system and method that balances these two important aspects of the image transfer process for a liquid or aqueous ink system. The system and method must also be capable of initiating and sustaining crashing, aggregating or precipitating of colorants in the liquid or aqueous ink after it is applied to the image transfer medium.